This line from the 2007 report’s chapter on human health is about as straightforward as any language can be: “Despite the known causal links between climate and malaria transmission dynamics, there is still much uncertainty about the potential impact of climate change on malaria at local and global scales.”

Now a study in this week’s edition of the journal Nature, “Climate Change and the Global Malaria Recession,” squarely concludes that the ongoing shrinkage of areas where the disease is endemic is many times more significant than any expansion of the potential malaria threat from climate change. It has two blunt conclusions:

First, widespread claims that rising mean temperatures have already led to increases in worldwide malaria morbidity and mortality are largely at odds with observed decreasing global trends in both its endemicity and geographic extent.

Second, the proposed future effects of rising temperatures on endemicity are at least one order of magnitude smaller than changes observed since about 1900 and up to two orders of magnitude smaller than those that can be achieved by the effective scale-up of key control measures. Predictions of an intensification of malaria in a warmer world, based on extrapolated empirical relationships or biological mechanisms, must be set against a context of a century of warming that has seen marked global declines in the disease and a substantial weakening of the global correlation between malaria endemicity and climate.

This paper is sure to please longtime critics of climate overstatement — reinforcing the reality that efforts to get attention that go beyond the science are bound to kick back. (This is as true for hoax promoters as it is for greenhouse campaigners.)

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By 2050 or so, the human population is expected to pass nine billion. Those billions will be seeking food, water and other resources on a planet where humans are already shaping climate and the web of life. Dot Earth was created by Andrew Revkin in October 2007 -- in part with support from a John Simon Guggenheim Fellowship -- to explore ways to balance human needs and the planet's limits.